Kristen Stewart was disappointed when she was told to tone down her Twilight sex scene with Robert Pattinson as the real-life couple wanted to behave like "animals" for the pivotal romp.

The actress wanted her onscreen lovemaking with Pattinson to be as raunchy as possible when she shot in character as a vampire for The Twilight Saga: Breaking Dawn - Part 2.

Speaking at the Twilight panel at California's Comic-Con event on Thursday, Stewart admitted she was told to restrain herself so the movie would be appropriate for younger audiences.

She told fans, "The ratings, man! (It's) a tricky thing... because we're supposed to have mind-boggling, otherworldly... sex. In the first one, Breaking Dawn 1, we really... this is weird... tried to keep the first one sweet. It's about self-discovery. Nothing about this series is raunchy. And I know that... But in the second one, we just wanted to be animals.

"We're not human anymore. How do you do that? We tried, and they told us it was rated R, and we were like (snaps fingers). So, yeah, that was that."